The use of blow-molded plastic containers has become commonplace in packaging beverages, such as juice. Blow-molded PET plastic containers are particularly useful in the so-called hot-fill process, i.e. filling the containers with beverages at an elevated temperature, sealing the containers, and then allowing the beverage to cool in the sealed container. Blow-molded PET plastic containers can provide a package with sufficient flexure to compensate for the changes of pressure and temperature, while maintaining structural integrity and aesthetic appearance. In addition, the plastic used in the containers is recyclable. Production of such containers can be achieved efficiently, quickly, and at a minimum of cost.
The major problem associated with hot-fillable blow-molded containers is the need to accommodate changes in the container configuration due to reductions in volume as the hot-filled liquid cools after the container has been capped. Prior art approaches to solving this problem involve the use of flex panels at various locations in the container sidewall. Flex panels are designed to move in response to reductions in volume in the containers.
It has also become known in the art to form grip panel structures within the flex panels. The grip panel structures provide easy container handling by a user, since they provide a place for a person's thumb and fingers to be received on opposite sides of the container when the person's palm engages a rear portion of the container. An example of a container having a grip panel within a flex panel is shown in U.S. Pat. No. 5,392,937, issued to the assignee of the present application.
It has been found, in practice, that the grip panels tend to distort under certain conditions encountered during the hot-fill process. For instance, tests have shown that during high-speed hot-fill of a 64 ounce blow-molded PET plastic container at a liquid temperature of 187.degree. F., and at flow rates in a range of 100 to 150 gpm (gallons per minute) the container must withstand a 4-6 psi (pounds per square inch) internal pressure for a brief period of time. The internal pressure acts on the grip panels, which are normally recessed into the container, and causes them to distort, e.g. bow outwardly from the container. Since the molecular structure of the plastic container is altered by changes in temperature and pressure, the grip panel cannot thereafter return to its initial designed state. This is unintended and is aesthetically undesirable.
Although the referenced patented container can function satisfactorily for its intended purpose under certain hot-fill conditions, there is a need for a blow-molded, grip-paneled plastic container which resists distortion of its inwardly recessed grip panels during high-speed hot-fill conditions.